Copper-based oxidation catalyst and its application

ABSTRACT

A copper-based oxidation catalyst comprising a substrate of copper or copper alloy and regions of a metal composed mainly of a group VIII element in close contact with the substrate, the surface of the substrate being partly exposed to the outside, has a high catalytic activity on the carbonyl oxidation reaction and is effective as a catalyst for electroless plating, a fuel cell electrode material, a catalyst for treating waste water or waste liquor or an oxidation reaction catalyst.

This application is a Continuation application of application Ser. No.08/458,676, filed Jun. 2, 1995 now abandoned which application is aDivisional application of application Ser. No. 08/124,076, filed Sep.21, 1993 now U.S. Pat. No. 5,457,079.

BACKGROUND OF THE INVENTION

1) Field of the Invention

The present invention relates to a copper-based oxidation catalysthaving a stable and catalytically highly active surface.

2) Related Art

It has been well known that the copper surface is active on oxidationreaction of formaldehyde, etc. and the copper surface has been appliedalso in catalysts for electroless copper plating, etc.

When electroless plating is applied to a non-conductive (dielectric)substrate, it is necessary to deposit a plating catalyst on thenon-conductive substrate in advance. Palladium is known as such acatalyst and is practically widely used. According to one procedure,palladium can be deposited on a non-conductive substrate by dipping anon-conductive substrate into an aqueous stannous chloride solutionacidified with hydrochloric acid, and then dipping the substrate into anaqueous palladium chloride solution acidified with hydrochloric acid,thereby carrying out a redox reaction on the surface of the substrateaccording to the following process:

    Pd.sup.++ +Sn.sup.++ →Pd+Sn.sup.++++

According to another procedure, a palladium colloid coated with stannousions is used as a plating catalyst.

In the foregoing procedures using a palladium catalyst, palladium metalinsoluble in an electroless plating solution may be released from thecatalyst-deposited substrate and entered into an electroless platingsolution, thereby giving rise to autolysis of the electroless platingsolution itself. Furthermore, particularly the procedure using both ofthe aqueous stannous chloride solution acidified with hydrochloric acidand the aqueous palladium chloride solution acidified with hydrochloricacid has a risk of attacking the substrate, because the solutions arehighly acidic. Still furthermore, the palladium catalyst belongs to anoble catalyst species, which makes the catalyst cost higher.

A copper colloid is known as another electroless plating catalystbesides the palladium. In the production of a printed circuit boardusing a copper colloid, for example, circuit formation on anon-conductive substrate by electroless plating, a plating resist isformed on non-circuit-destined parts, a copper colloid is deposited oncircuit-destined parts and also on the plating resist, and then thecopper colloid catalyst on the plating resist is removed by mechanicalpolishing (JP-A-62-271491). In that case, the copper colloidcatalyst-deposited non-conductive substrate is dried by heating at100°-160° C. to enhance the adhesion between the surface of thenon-conductive substrate and the copper colloid catalyst. The driedcopper catalyst is in an oxidized state and has no catalytic activity,and thus is subjected to a reduction treatment by a reducing agent. Inthe electroless plating using such a copper colloid catalyst, it takesmuch time in starting of electroless plating reaction. Alternatively, anactive electroless plating solution, that is, an unstable electrolessplating solution, must be used, as disclosed in JP-A 62-297472, page 6,line 19-page 7, line 2.

An aqueous solution of copper colloid catalyst can be prepared by addingdimethylamineborane to an aqueous solution containing copper ions,gelatin and polyethylene glycol at a pH of 1 to 2, thereby reducing thecopper ions to metallic copper, and then adjusting the aqueous solutionto a pH of 2 to 4, as disclosed, for example, in JP-A 61-23762.

Furthermore, a combination of copper and nickel is disclosed in JP-A2-207844 as a catalyst for electrolytic reduction of carbon dioxide,etc. The catalyst is a reduction catalyst for electrolytically reducinga reducible compound such as carbon dioxide or carbon monoxide under areduction potential substantially equal to the theoretical potential,thereby forming useful compounds such as methane, ethylene, etc.

Copper surface is very susceptible to oxidation, and, once oxidized, hasno catalytic activity. Even if reduced, the resulting copper surface hasa considerably poor activity, as compared with noble metal catalystssuch as platinum, palladium, etc.

Nickel, on the other hand, has a high corrosion resistance and noactivity on the oxidation reaction of formaldehyde, etc.

In the above-mentioned prior art procedure using a copper colloidcatalyst, the copper colloid deposited on a non-conductive substrate isreadily oxidized by exposure to the atmospheric air and deactivated.Deactivation of the copper colloid catalyst is considerable particularlywhen heated to 100° to 160° C., and complete reactivation is hard toobtain even by using a reducing agent. Metallic copper itself has a poorcatalytic activity, and, when used as a plating catalyst, parts where noplating reaction takes place, that is, the so called platingnon-deposited parts are highly liable to appear. Thus, the coppercolloid catalyst has not been so far widely utilized.

It is also known that the metallic copper has an activity on theoxidation reaction of lower alcohols as a fuel for a fuel cell, such asmethanol, etc. However, its activity is considerably lower than that ofnoble metals such as platinum, palladium, etc., and thus the metalliccopper has not been so far utilized as an electrode material for a fuelcell.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a copper-basedoxidation catalyst having a high corrosion resistance and a highactivity.

Another object of the present invention is to provide a copper-basedcatalyst for electroless plating having a distinguished catalyticactivity without autolysis of an electroless plating solution.

Other object of the present invention is to provide an electrodematerial for a fuel cell.

Further object of the present invention is to provide a copper-basedoxidation catalyst capable of converting the globalenvironment-polluting substances or harmful substances such asaldehydes, etc. to other harmless substances by oxidation.

According to the present invention, these objects can be attained by:

(1) A copper-based oxidation catalyst, which comprises a substrate ofcopper or copper alloy and regions comprising a metal composed mainly ofa group VIII element or its oxide in close contact with the substrate,the surface of the substrate being partly exposed to the outside;

(2) A copper-based oxidation catalyst, which comprises a substrate,which surface is made of copper or copper alloy, and regions of a metalcomposed mainly of a group VIII element or its oxide in contact with thesurface of the substrate, the surface of the substrate being partlyexposed to the outside.

(3) The above-mentioned copper-based oxidation catalysts wherein acovering ratio of coverage area of the metal composed mainly of thegroup VIII element or its oxide to the effective surface area of thesubstrate is 0.01 to less than 1.

(4) The above-mentioned copper-based oxidation catalysts wherein themetal composed mainly of the group VIII element or its oxide are in theform of a film having a thickness of 1 to 5 nm;

(5) The above-mentioned copper-based oxidation catalysts wherein themetal composed mainly of the group VIII element or its oxide is nickel,cobalt or iron or its oxide; and

(6) The above-mentioned copper-based oxidation catalysts wherein thesubstrate is in the form of fine particles, foamed mass, thin film plateor honeycomb structure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view showing one example of anickel deposition state on the surface of the present copper-basedoxidation catalyst.

FIG. 2 is a current-potential curve diagram of formaldehyde oxidationreaction at a copper electrode and a nickel-coated copper electrodeaccording to Example 1.

FIG. 3 is a diagram showing relations between nickel electrolyticplating time and formaldehyde oxidation peak current at a nickel-coatedcopper electrode according to Example 1.

FIG. 4 is a diagram showing relations between iron electrolytic platingtime and formaldehyde oxidation peak current at an iron-coated copperelectrode according to Example 3.

FIG. 5 is a diagram showing relations between cobalt electrolyticplating time and formaldehyde oxidation peak current at a cobalt-coatedcopper electrode according to Example 4.

FIG. 6 is a schematic cross-sectional view showing the structure of anelectrolytic cell for waste water treatment.

FIG. 7 is a schematic view showing the key structure of a methanol fuelcell.

DETAILED DESCRIPTION OF THE INVENTION

A covering ratio of less than 1 defined in the foregoing item (3)designates such a state that a substrate of metallic copper coated witha coating metal selected from the group VIII metal elements still haschemical properties same as those of copper and not identical with thoseof the coating metal. That is, a coating metal film may be in the formof a porous thin film or the coating metal is in an island form shown inFIG. 1, where nickel islands 1 are discretely distributed on the surfaceof a copper substrate 2, while exposing the surface of the substrate tothe outside through between the nickel islands. Complete coating orcoverage of the copper metal substrate surface with the coating metalcannot attain the above-mentioned objects of the present invention. Inother words, it is important that copper or copper alloy as a substrateis partly exposed to the outside. That is, even if the entire surface ofthe substrate of metallic copper seems to have been coated with thecoating metal from the viewpoint of the amount of electric currentrequired for the electroplating process, vapor deposition time requiredfor the vapor deposition process, etc., the substrate of metallic coppercoated with the film of the coating metal can be used so far as it canstill shows the same properties as those of substrate copper. A coveringratio of less than 0.01 is not preferable, because no catalytic activityas an oxidation catalyst is fully obtained.

As a coating metal, the group VIII metal elements can be used. Nickel,cobalt and iron are preferable from the viewpoint of their cost, andthey can be used in the oxide form.

The metallic copper substrate can be coated with nickel, cobalt or ironby electroplating, electroless plating, vapor deposition, sputtering,etc. Particularly, electroplating is preferable, because the coveringratio can be controlled by adjusting an amount of electric currentrequired for the electroplating. Colloid particles of metallic coppercan be readily coated with nickel, cobalt or iron by adding a reducingagent such as dimethylamineborane, etc. to a copper colloid solution,and adding an aqueous solution containing ions of nickel, cobalt or ironthereto.

Catalyst particles coated with nickel, cobalt or iron in the islandforms on the surfaces of colloid particles, as shown in FIG. 1, can beobtained, for example, by controlling the amount of metallic ions ofnickel, cobalt or iron to be added to less than the amount of copper inthe copper colloid solution. Furthermore, the covering ratio of nickel,cobalt or iron on copper colloid particle can be estimated from theentire surface of copper colloid obtained from particle sizes andconcentration of copper colloid particles and moles of ions of nickel,cobalt or iron to be added, and thus the covering ratio can becontrolled. For example, a copper colloid catalyst coated with nickel ina covering ratio of 0.5 can be obtained by adding about 0.01 mole ofnickel ions to a copper colloid solution containing copper particles,0.1 μm in radius, prepared from one mole of copper.

In case of electroless copper plating, a copper-plated substrate with agood plating adhesion can be obtained by depositing the catalyst onto anonconductive substrate according to the ordinary procedure.

In case of converting global environment-polluting substances such asaldehydes or harmful substances to other harmless substances, theconversion can be carried out in an electrolytic cell using an electrodeof copper substrate in the plate form or the honeycomb form, coated witha coating material such as nickel or the like in a covering ratio ofless than 1 by electroplating, electroless plating, vapor deposition,sputtering, etc.

FIG. 6 is a schematic view of the structure of an electrolytic cell 4for oxidizing a waste water. When waste water 7 containing formaldehydeas a harmful substance is electrolytically oxidized to formic acid, ahydrogen gas is generated at a catalyst-modified electrode 5 (anode),which is modified with the catalyst, on the basis of oxidation reactionof formaldehyde, and a hydrogen gas is generated at a counter electrode6 (cathode) on the basis of water. These hydrogen gases, when collectedthrough a generated gas collector duct 9 open to a hood 8 for theelectrolytic cell 4, can be reutilized as clean hydrogen energy withoutgenerating CO₂. As the necessary electric energy for the electrolysis,natural energy from a solar cell 10, or the like can be utilized,whereby an effective system for treating waste water can be completed.The catalyst-modified electrode, when used as a fuel electrode for afuel cell, is in a structure comprising a copper substrate in the plateor honeycomb form, coated with nickel or the like in a covering ratio ofless than 1, as in that for the above-mentioned electrlytic cell.

FIG. 7 illustrates essential structural members of an efficient, lowcost methanol-type fuel cell, which comprises a catalyst-modified fuelelectrode 11 as an electrode for oxidizing methanol and an air electrode13 as an oxidizing electrode, provided in a fuel chamber 15 and anelectrolytic chamber 14, respectively, through an electrolyte layer 12.

In the electroless copper plating, carbonyls such as formaldehyde andglyoxylic acid are often used as a reducing agent for reducing copperions in the electroless plating solution. Electroless plating proceedsaccording to a redox reaction between the reducing agent and metal ionsin the electroless plating solution. The reaction proceeds only on thecatalyst on the surface of a material to be plated. That is, noelectroless plating reaction proceeds unless the surface of a materialto be plated has a catalytic oxidation activity on carbonyls.

Generally, the electroless plating solution is a highly alkalinesolution having a pH of about 12, and palladium, platinum, gold, silver,copper, etc. are known as metals having a catalytic activity on theoxidation reaction of carbonyls in the solution. In the electrolesscopper plating, a copper catalyst is distinguished particularly becauseit will not contaminate the electroless copper solution, though itscatalytic activity is very low.

On the other hand, the group VIII metals of the periodic table, such asnickel, cobalt and iron, have a surface of hydroxide or oxide under acarbonyl oxidation-occasioning potential in an alkaline solution havinga pH of about 12, and thus are quite inert to the carbonyl oxidation.

According to the present invention the catalytic activity on theoxidation reaction can be considerably increased, as compared with thatof copper, by coating copper, which has a low catalytic activity on theelectrolytic carbonyl oxidation reaction, with nickel, cobalt, iron orthe like, which is inert to the reaction, in a covering ratio of lessthen 1. Reasons why the catalytic activity on the oxidation reaction canbe considerably increased by coating copper with quite an inert metalsuch as nickel or like in a covering ratio of less than 1 can beexplained as follows:

That is, it seems that the carbonyl electrolytic oxidation reactionproceeds according to the following reaction mechanism:

    HCHO+H.sub.2 O→CH.sub.2 (OH).sub.2                  (1)

    CH.sub.2 (OH).sub.2 +OH→CH.sub.2 OHO+H.sub.2 O      (2)

    CH.sub.2 OHO→CHOHO+H                                (3)

    CHOHO+OH→HCOO+H.sub.2 O+e                           (4)

    H+OH→H.sub.2 O+e                                    (5)

    H+H→H.sub.2                                         (6)

Alcoholate ions (CH₂ OHO⁻) formed by the disproportionation reaction areadsorbed onto the catalyst surface and also hydrogen atoms are adsorbedonto the catalyst surface at the same time. Then, the alcoholate ionsadsorbed on the catalyst surface turn to carboxylate ions (HCOO⁻)through electron migration.

On the other hand, the adsorbed hydrogen atoms turn to water or ahydrogen gas according to the above-mentioned equation (5) or (6). Thereaction route of adsorbed hydrogen atoms via the above-mentionedequation (5) is accompanied with electron migration, and thus thecarbonyl oxidation reaction belongs to a dielectronic reaction, as shownby the following equation (7), whereas the reaction route of adsorbedhydrogen via the above-mentioned equation (6) belongs to amonoelectronic reaction, as shown by the following equation (8):

    HCHO+3OH→HCOO+2H.sub.2 O+2e                         (7)

    HCHO+2CH→HCOO+H.sub.2 O+1/2H.sub.2 ↑+e        (8)

Generally, palladium and platinum perform the dielectronic reaction,whereas gold, silver and copper perform the monoelectronic reaction. Thepresent copper-based oxidation catalyst can be presumed to perform themonoelectronic reaction, because generation of a hydrogen gas isobservable on the catalysts surface during the reaction. That is, it canbe presumed that the reaction proceeds through the same reactionmechanism as that on the copper surface, but with a higher catalyticactivity for the following reasons. It seems that the reaction to form ahydrogen gas through recombination of hydrogen atoms, as shown by theabove-mentioned equation (6), proceeds slowly on the copper surface, butfaster on the surface of such a metal as nickel. The reaction proceedslike the so called Tafel reaction, one of basic reactions in thehydrogen electrode reactions in the electrochemical field. It is saidthat the Tafel reaction proceed slowly on a copper surface, but fasteron a nickel surface. That is, the reaction shown by the above-mentionedequation (6) proceeds smoothly on the present copper-based oxidationcatalyst comprising a copper substrate coated with nickel in a coveringratio of less than 1, and thus it seems that the catalytic activity isincreased in the present invention.

The present copper-based oxidation catalyst can be used in a broad fieldincluding an electroless plating catalyst, a fuel cell electrode, acatalyst for treating waste water or liquor, etc.

PREFERRED EMBODIMENTS OF THE INVENTION

The present invention will be described in detail below, referring toExamples.

Example 1

A copper electrode having an area of 1 cm² was subjected to soft etchingin an etching solution containing 200 g/l of ammonium peroxodisulfateand 20 g/l of sulfuric acid at 35° C. for 2 hours, thereby cleaning thesurface of copper electrode. Then, the copper electrode was dipped in anickel plating solution containing 220 g/l of nickel (II) sulfatehexahydrate, 15 g/l of boric acid and 15 g/l of sodium chloride,adjusted to a pH of 5.2 to 5.8 with sodium hydroxide and subjected tonickel electrolytic plating at a current density of 0.05 mA/cm², whilecontrolling a covering ratio of nickel on the copper electrode surfaceby adjusting the plating time.

Electrolytic oxidation reaction of formaldehyde in an aqueous 1N sodiumhydroxide solution containing 0.2 mol/l of formaldehyde with the thusobtained nickel-coated copper electrode was investigated according to apotential sweep method by applying an electrode potential of -1.1 V to-0.45 V to the electrode at a sweep rate of 50 mV/sec and measuring theresulting oxidation current of formaldehyde. The results are shown inFIG. 2.

FIG. 2 shows changes in the electrolytic oxidation current offormaldehyde, where curve A shows the case of naked copper electrode andcurve B the case of nickel-coated copper electrode. Nickel plating timefor obtaining the nickel-coated copper electrode was 5 seconds, and thecovering ratio of nickel was estimated to be about 0.68 from the amountof electric current required for the plating. It was also confirmed thatformaldehyde was oxidized to formic acid.

It is apparent from FIG. 2 that the peak of formaldehyde oxidationcurrent on the nickel-coated copper electrode is about 7 mA/cm², whichis about 3 times as large as that on the naked copper electrode. Theelectrode potential under which the oxidation current starts to flow isshifted by about 0.3 V towards the cathode, and an overvoltage due tothe formaldehyde oxidation is reduced.

As shown above, it was observed that the catalytic activity wasremarkably increased by coating the copper electrode with nickel(covering ratio=0.68).

Formaldehyde oxidation current was investigated with nickel-coated coperelectrodes prepared in the same manner as above, except that the nickelplating time was changed in a range of 0 to 5 minutes. The results areshown in FIG. 3.

Catalytic formaldehyde oxidation activity of the nickel-coated copperelectrode with a nickel plating time of about 120 seconds wassubstantially equal to that of naked copper electrode, and the catalyticoxidation activity with nickel-coated copper electrode with a platingtine of more than 120 seconds was less than that of the naked copperelectrode, because it seems that the copper electrode surface was fullycoated with nickel inert to the oxidation reaction, whereby the catalystsurface fully turned to the nickel metal surface.

With a plating time of less than 120 seconds, the catalytic oxidationactivity was observable. Nickel plating at a current density of 0.05mA/cm² would be able to fully coat the entire copper electrode surfacewith nickel with a plating time of about 10 seconds. However, actualobservation of higher catalytic activity of nickel-coated copperelectrode than that of naked copper electrode seems to be due to nickelcoating in the island form being on the copper electrode substrate, asshown in FIG. 1.

It is apparent from this Example that the nickel-coated copper electrodein a covering ratio of nickel of less than 1 has a higher catalyticactivity on the electrolytic formaldehyde oxidation reaction.

Comparative Example 1

A copper electrode having a area of 1 cm² was subjected to soft etchingin an etching solution containing 200 g/l of ammonium peroxodisulfateand 20 g/l of sulfuric acid at 35° C. for 2 minutes in the same manneras in Example 1, thereby cleaning the surface of copper electrode.

Electrolytic oxidation reaction of formaldehyde in an aqueous 1N sodiumhydroxide solution containing 0.2 mol/l of formaldehyde with the thusprepared copper electrode was investigated according to a potentialsweep method. It was found that the peak of oxidation current based onthe formaldehyde oxidation reaction on the naked copper electrode was1.8 mA/cm², which was about 1/4 times as small as that of thenickel-coated copper electrode (covering ratio of nickel: 0.68) ofExample 1.

Comparative Example 2

A nickel electrode having an area of 1 cm² was subjected to soft etchingin an aqueous 4N nitric acid solution at 30° C. for one minutes, therebycleaning the surface of nickel electrode.

Electrolytic oxidation reaction of formaldehyde in an aqueous 1N sodiumhydroxide solution containing 0.2 mol/l of formaldehyde with the thusprepared nickel electrode was investigated according to a potentialsweep method. It was found that no oxidation current based on theformaldehyde oxidation reaction was observed at all, and thus noformaldehyde oxidation reaction took place at all on the nickelelectrode.

Example 2

0.15 moles of nickel (II) sulfate was added to 1 l of an aqueous coppercolloid solution containing 1 mol/l of metallic copper and 10 g/l ofdimethylamineborane as a reducing agent, thereby preparing anickel-coated copper colloid catalyst.

Then, a fiber glass-reinforced epoxy resin substrate havingthroughholes, 0.5 mm in diameter, was dipped in the nickel-coated coppercolloid solution, and then the throughhole walls of the epoxy resinplate were subjected to electroless copper plating in an electrolesscopper plating solution having the following composition at a solutiontemperature of 72° C. It was found that the throughhole walls werecompletely coated with a copper plating film:

    ______________________________________                                        CuSO.sub.4  5H.sub.2 O    10 g/l                                              Disodium ethylene diaminetetraacetate                                                                   30 g/l                                              Aqueous 37% HCHO Solution (formalin)                                                                     3 ml/l                                             NaOH                      12 g/l                                              2,2'-dipyridyl            30 mg/l                                             Polyethylene glycol       10 g/l                                              (average molecular weight: 600)                                               ______________________________________                                    

Comparative Example 3

Throughhole walls of glass fiber-reinforced epoxy resin substrate weresubjected to electroless copper plating in the same manner as in Example2 except that a copper colloid catalyst without nickel coating was usedin place of the nickel-coated copper colloid catalyst. Relations betweenthe preservation time in air right after the catalyst deposition bydipping in the copper colloid catalyst solution to the start ofelectroless plating and the state of electroless plating wereinvestigated for the nickel-coated copper colloid catalyst and thenickel-noncoated copper colloid catalyst and the results are given inthe following Table.

    ______________________________________                                        Nickel plating on                                                             copper colloid                                                                              Preservation time (days)                                        catalyst      0.5   1       2   3     5   7                                   ______________________________________                                        Done (Ni covering                                                                           ∘                                                                       ∘                                                                         ∘                                                                     ∘                                                                       ∘                                                                     ∘                       ratio: 0.68)                                                                  None          Δ                                                                             x       x   x     x   x                                   ______________________________________                                         ∘: Uniform plating                                                Δ: Partially uneven plating                                             n: uneven plating                                                        

It was found neither non-deposition of plating nor uneven plating wasobserved at all in case of the nickel-coated copper colloid catalysteven when the substrate was preserved in air for one week after thecatalyst deposition, and good plating films could be obtained with agood oxidation resistance in air.

Example 3

Copper electrodes whose surfaces were cleaned in the same manner as inExample 1 were dipped in an aqueous iron plating solution containing 30g/l of ferric chloride and subjected to electrolytic iron plating at acurrent density of 0.05 mA/cm², while controlling the iron coveringratio by adjusting the plating time in the same manner as that for thenickel plating.

Electrolytic oxidation reaction of formaldehyde in an aqueous 1N sodiumhydroxide solution containing 0.2 mol/l of formaldehyde with the thusiron-coated copper electrodes was investigated according to a potentialsweep method. Relations between the iron electrolytic plating time andthe peak current of electrolytic oxidation reaction are shown in FIG. 4.When the electrolytic iron plating time is less than 100 seconds, anoxidation current peak was observed in the same manner as in the case ofthe nickel-coated copper electrode.

Example 4

Copper electrodes whose surfaces were cleaned in the same manner as inExample 1 were dipped in an aqueous cobalt solution containing 15 g/l ofcobalt sulfate and subjected to electrolytic cobalt plating at a currentdensity of 0.05 mA/cm², while controlling the cobalt covering ratio byadjusting the plating time in the same manner as that for the nickelplating.

Catalytic activity of the thus obtained cobalt-coated copper electrodeson the electrolytic oxidation reaction of formaldehyde was investigatedin the same manner as in Example 1. Relations between the electrolyticcobalt plating time and the peak current of electrolytic oxidationreaction are shown in FIG. 5. When the electrolytic plating time is lessthan 100 seconds, an oxidation current peak was observed in the samemanner as in the case of the nickel-coated copper electrode.

Example 5

Catalytic activity of nickel-coated copper electrodes prepared in thesame manner as in Example 1 on methanol electrolytic oxidation reactionwas evaluated. Good results were obtained.

The present copper-based oxidation catalyst comprising a copper-basedmetal substrate coated with a group VIII transition metal in a coveringratio of less than 1 has a high catalytic activity on carbonyl oxidationreaction and is effective as a catalyst for electroless plating, a fuelcell electrode material or a catalyst for treating waste water or wasteliquor. Particularly, nickel, cobalt and iron are available at a lowcost and thus preferable among the group VIII transition metals.

What is claimed is:
 1. An apparatus for waste water treatment, whichcomprises a cell for electrolytic oxidation treatment having a pair ofelectrodes including an anode and a cathode for forming a circuitconnected to an external power source and being filled with waste water,the anode comprising copper or copper alloy having a porous filmcomposed of a member selected from the group consisting of nickel,cobalt, iron and an oxide thereof on the surface.
 2. An apparatusaccording to claim 1, wherein the porous film has a thickness of from 1to 5 nm.
 3. An apparatus according to claim 1, wherein the porous filmhas a covering ratio of coverage area of the film to an effectivesurface area of the surface of the copper or copper alloy of 0.1 to lessthan 1.